Pre-positioning data in a network memory appliance

CROSS-REFERENCES

This nonprovisional United States patent application is a continuation-in-part of nonprovisional U.S. patent application Ser. No. 11/202,697 filed Aug. 12, 2005 and entitled “Network Memory Architecture,” which is hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates generally to network memory and more particularly to a network memory architecture.

2. Description of Related Art

To allow remote employees access to an enterprise's information systems, organizations typically choose between two networking approaches: centralized servers or distributed servers. Centralized server implementations have the advantage of simplicity since an information technology (IT) professional centrally manages, maintains, and enforces policies for the organization's data.

<figref idref="DRAWINGS">FIG. 1</figref> illustrates a centralized server system <b>100</b> in the prior art. The centralized server system <b>100</b> includes a branch office <b>110</b> and a central office <b>120</b> coupled by a communication network <b>130</b>. The communication network <b>130</b> forms a WAN between the branch office <b>110</b> and the central office <b>120</b>.

Typically, the central servers <b>160</b> in the central office <b>120</b> store the organization's data. Computers <b>140</b> make requests for the data from the central servers <b>160</b> over the communication network <b>130</b>. The central servers <b>160</b> then return the data to the computers <b>140</b> over the communication network <b>130</b>.

The communication network <b>130</b> typically comprises a private network (e.g., a leased line network) or a public network (e.g., the Internet). The connections to the communication network <b>130</b> from the branch office <b>110</b> and the central office <b>120</b> typically cause a bandwidth bottleneck for exchanging the data over the communication network <b>130</b>. The exchange of the data between the branch office <b>110</b> and the central office <b>120</b>, in the aggregate, will usually be limited to the bandwidth of the slowest link in the communication network <b>130</b>.

For example, the router <b>150</b> connects to the communication network <b>130</b> by a T1 line, which provides a bandwidth of approximately 1.544 Megabits/second (Mbps). The router <b>170</b> connects to the communication network <b>130</b> by a T3 line, which provides a bandwidth of approximately 45 Megabits/second (Mbps). Even though the communication network <b>130</b> may provide an internal bandwidth greater than 1.544 Mbps or 45 Mbps, the available bandwidth between the branch office <b>110</b> and the central office <b>120</b> is limited to the bandwidth of 1.544 Mbps (i.e., the T1 connection). Connections with higher bandwidth to relieve the bandwidth bottleneck across the communication network <b>130</b> are available, but are generally expensive and have limited availability.

Moreover, many applications do not perform well over the communication network <b>130</b> due to the limited available bandwidth. Developers generally optimize the applications for performance over a local area network (LAN) which typically provides a bandwidth between 10 Mbps to Gigabit/second (Gbps) speeds. The developers of the applications assume small latency and high bandwidth across the LAN between the applications and the data. However, the latency across the communication network <b>130</b> typically will be 100 times that across the LAN, and the bandwidth of the communication network <b>130</b> will be 1/100th of the LAN.

Alternatively, many organizations select the distributed server implementation to mitigate some of the problems with the centralized server implementation. <figref idref="DRAWINGS">FIG. 2</figref> illustrates a distributed server system <b>200</b> in the prior art. The distributed server system <b>200</b> includes a branch office <b>210</b>, a central office <b>220</b>, and a communication network <b>230</b>. The communication network <b>230</b> forms a WAN between the branch office <b>210</b> and the central office <b>220</b>.

In the distributed server system <b>200</b>, the branch servers <b>240</b> (e.g., email servers, file servers and databases) are placed locally in the branch office <b>210</b>, rather than solely in the central office <b>220</b>. The branch servers <b>240</b> typically store all or part of the organization's data. The branch servers <b>240</b> generally provide improved application performance and data access. The branch servers <b>240</b> respond to a request for the organization's data from the local data. For each request for the data, the central servers <b>270</b> potentially do not need to transfer the data over the communication network <b>130</b> (i.e., the WAN). Synchronization and backup procedures are implemented to maintain the coherency between the local data in the branch office <b>210</b> and the data in the central office <b>220</b>.

Unfortunately, managing the distributed server system <b>200</b> is complex and costly. From a physical point of view, the distributed server system <b>200</b> with one hundred branch offices requires an order of one hundred times more equipment than the centralized server approach. Each piece of the equipment not only needs to be purchased, but also installed, managed, and repaired driving significant life cycle costs. The branch office <b>210</b> may need additional local IT personnel to perform operations because of this “Server Sprawl”. Furthermore, the multiplication of managed devices means additional license costs, security vulnerabilities, and patching activities.

In distributed server implementations (e.g., the distributed server system <b>200</b>), the data, including the “golden copy” or most up-to-date version of mission critical data, is often stored (at least temporarily) only on the branch servers <b>240</b> in the branch office <b>210</b>. Organizations implement complex protocols and procedures for replication and synchronization to ensure that the mission critical data is backed up and kept in-sync across the WAN with the central servers <b>270</b>.

Furthermore, although <figref idref="DRAWINGS">FIG. 1</figref> and <figref idref="DRAWINGS">FIG. 2</figref> illustrate a single branch office and a single central office, multiple branch offices and multiple central offices exacerbate the previously discussed problems. For example, in a centralized server implementation having multiple branches, computers in each of the multiple branch offices make requests over the WAN to central servers for the organization's data. The data transmitted by the central servers in response to the requests quickly saturate the available bandwidth of the central office's connection to the communication network, further decreasing application performance and data access at the multiple branch offices. In a distributed server implementation having multiple branches, the cost to provide branch servers in each of the multiple branch offices increases, as well as the problems of licensing, security vulnerabilities, patching activities, and data replication and synchronization. Moreover, different branches may simultaneously attempt to modify the same piece of information. Maintaining coherency in a distributed implementation requires complex and error prone protocols.

As well as implementing centralized servers or distributed servers, organizations also implement mechanisms for caching to improve application performance and data access. A cache is generally used to reduce the latency of the communication network (e.g., communication network <b>230</b>) forming the WAN (i.e., because the request is satisfied from the local cache) and to reduce network traffic over the WAN (i.e., because responses are local, the amount of bandwidth used is reduced).

Web caching, for example, is the caching of web documents (i.e., HTML pages, images, etc.) in order to reduce web site access times and bandwidth usage. Web caching typically stores local copies of the requested web documents. The web cache satisfies subsequent requests for the web documents if the requests meet certain predetermined conditions.

One problem with web caching is that the web cache is typically only effective for rarely modified static web documents. For dynamic documents, there is a difficult trade off between minimizing network traffic and the risk of the web cache serving up stale data. The web cache may serve stale data because the web cache responds to requests without consulting the server.

Another problem is that the web cache does not recognize that two otherwise identical documents are the same if they have different Uniform Resource Locator (URL). The web cache does not consider the content or context of the documents. Thus, the web cache caches the documents by URL or filename without a determination of the content or context of the document. Moreover, the web cache stores entire objects (such as documents) and cache-hits are binary: either a perfect match or a miss. Even where only small changes are made to the documents, the web cache does not use the cached copy of the documents to reduce network traffic.

SUMMARY OF THE INVENTION

The invention addresses the above problems by providing a network memory system and method implemented by the system. A network memory system comprises a first appliance and a second appliance. The first appliance receives data and determines whether a portion of the data is locally accessible to the second appliance. The first appliance generates an instruction based on the determination and transfers the instruction to the second appliance over a communication network. The second appliance receives the instruction from the first appliance over the communication network and processes the instruction to obtain the data. The second appliance then transfers the data to a computer.

Advantageously, the first appliance may not transfer the data over the communication network if the data is locally accessible to the second appliance. Based on the instruction, the second appliance obtains the data and transfers the data to the computer. In one embodiment, the communication network may comprise a wide area network (WAN). The network memory system effectively reduces latency over the communication network, and reduces network traffic by minimizing the amount of data sent over the communication network. In a further advantage, the first appliance may assume the role of the second appliance, and the second appliance may assume the role of the first appliance, thereby reducing network traffic and latency for uni-directional and bi-directional communication over the communication network. The second appliance receives the data and determines whether a portion of the data is locally accessible to the first appliance. The second appliance generates another instruction based on the determination and transfer the another instruction to the first appliance over the communication network. The first appliance receives the another instruction from the second appliance over the communication network and process the another instruction to obtain the data. The first appliance then transfers the data to another computer.

In some embodiments, the first appliance generates the instruction indicating to store the data in a database. The instruction may also indicate to retrieve the data from the database. In some embodiments, the first appliance may generate a plurality of instructions. The plurality of instructions may indicate a plurality of indexes for retrieving the data. The instruction may also indicate an index within the database for the data. Accordingly, the second appliance may store the data in the database based on the instruction. The second appliance may retrieve the data in the database based on the instruction.

The first appliance may transfer to the second appliance a portion of the data that is not locally accessible. The second appliance receives the transferred portion of the data, retrieves the portion of the data that is locally accessible to the second appliance, and processes the portions to obtain the data. The first appliance may receive the data from a computer server. The second appliance may also transfer the data to the computer based on a request for the data over the communication network by the computer. The network memory system therefore provides the advantages and simplicity of centralized data storage, with the ability to quickly retrieve locally accessible data.

Further, in some embodiments, the first appliance further determines whether the data is locally accessible to a third appliance. The first appliance then generates another instruction to the third appliance based on the determination and transfers the another instruction to the third appliance over the communication network. The third appliance receives the another instruction from the first appliance over the communication network and processes the another instructions to obtain the data. The third appliance then transfers the data to another computer. Furthermore, the network memory system may localize a copy of the data in multiple appliance/node implementations without the license fees and expenses, maintenance, and security costs of distributed server hardware.

Further embodiments comprise a pre-positioning controller that executes a pre-positioning command to send data through at least one network memory appliance to a pre-positioning server. The network memory appliance stores the data for positioning in the network memory. The pre-positioning command may indicate a time of transmission of the data and/or be regularly scheduled. The pre-positioning receiver may comprise a file transfer protocol server, a hypertext transfer protocol server, and/or a file system server. In various embodiments, the pre-positioning receiver may emulate a file transfer protocol server, a hypertext transfer protocol server, and/or a file system server.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> illustrates a centralized server system in the prior art;

<figref idref="DRAWINGS">FIG. 2</figref> illustrates a distributed server system in the prior art;

<figref idref="DRAWINGS">FIG. 3</figref> illustrates a network memory system, in an exemplary implementation of the invention;

<figref idref="DRAWINGS">FIG. 4</figref> illustrates a message sequence chart for the network memory system where a response to a data request is not locally accessible to a branch appliance, in an exemplary implementation of the invention;

<figref idref="DRAWINGS">FIG. 5</figref> illustrates data structures for the network memory system to determine whether a portion of the data is locally accessible to the branch appliance, in an exemplary implementation of the invention;

<figref idref="DRAWINGS">FIG. 6</figref> illustrates a message sequence chart for the network memory system where the response to the data request is locally accessible to the branch appliance, in an exemplary implementation of the invention;

<figref idref="DRAWINGS">FIG. 7A</figref> and <figref idref="DRAWINGS">FIG. 7B</figref> illustrate a message sequence chart for the network memory system where a portion of the response to the data request is locally accessible to the branch appliance, in an exemplary implementation of the invention;

<figref idref="DRAWINGS">FIG. 8</figref> illustrates a block diagram of the branch appliance, in an exemplary implementation of the invention;

<figref idref="DRAWINGS">FIG. 9</figref> illustrates a block diagram of a central appliance, in an exemplary implementation of the invention;

<figref idref="DRAWINGS">FIG. 10</figref> illustrates a network memory system between a first office, a second office, and a third office, in an exemplary implementation of the invention; and

<figref idref="DRAWINGS">FIG. 11</figref> illustrates a message sequence chart for the network memory system for discovery and reconciliation, in an exemplary implementation of the invention.

<figref idref="DRAWINGS">FIG. 12</figref> depicts a diagram of an exemplary network memory system in which various embodiments of the present invention may be practiced;

<figref idref="DRAWINGS">FIG. 13</figref> depicts a block diagram of a pre-positioning command according to exemplary embodiments;

<figref idref="DRAWINGS">FIG. 14</figref> depicts a flowchart illustrating a process performed by a pre-positioning controller for pushing data to a pre-positioning receive according to exemplary embodiments; and

<figref idref="DRAWINGS">FIG. 15</figref> depicts a message sequence chart of the signals transferred upon execution of a pre-positioning command.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments discussed herein are illustrative of one example of the present invention. As these embodiments of the present invention are described with reference to illustrations, various modifications or adaptations of the methods and/or specific structures described may become apparent to those skilled in the art. All such modifications, adaptations, or variations that rely upon the teachings of the present invention, and through which these teachings have advanced the art, are considered to be within the scope of the present invention. Hence, these descriptions and drawings should not be considered in a limiting sense, as it is understood that the present invention is in no way limited to only the embodiments illustrated.

To provide improved application performance and data access, the network memory system generally comprises a first appliance and a second appliance. The first appliance receives data and determines whether a portion of the data is locally accessible to the second appliance. The first appliance generates an instruction based on the determination and transfers the instruction to the second appliance through the communication network.

The network memory system provides that the second appliance processes the instruction to obtain the data and transfers the data to a computer. The data may be locally accessible to the second appliance, and the transfer to the computer may occur faster than transferring the data over the communication network. Accordingly, the second appliance transfers the data to computer without the first appliance transferring the data over the communication network that may have a high latency and low bandwidth. Thus, the network memory system operates to reduce latency and network traffic over the communication network.

<figref idref="DRAWINGS">FIG. 3</figref> illustrates a network memory system <b>300</b>, in an exemplary implementation of the invention. The network memory system <b>300</b> includes a branch office <b>310</b>, a central office <b>320</b>, and a communication network <b>330</b>. The branch office <b>310</b> includes computers <b>340</b>, a branch appliance <b>350</b>, and a router <b>360</b>. The central office <b>320</b> includes central servers <b>370</b>, a central appliance <b>380</b>, and a router <b>390</b>.

In the branch office <b>310</b>, the computers <b>340</b> are linked to the branch appliance <b>350</b>. The branch appliance <b>350</b> is linked to the router <b>360</b>. The router <b>360</b> is coupled to the communication network <b>330</b>. In the central office <b>320</b>, the central servers <b>370</b> are linked to the central appliance <b>380</b>. The central appliance <b>380</b> is linked to the router <b>390</b>. The router <b>390</b> is coupled to the communication network <b>330</b>.

The principles discussed herein are equally applicable to multiple branch offices (not shown) and to multiple central offices (not shown). For example, the network memory system <b>300</b> may include multiple branch offices and/or multiple central offices coupled to the communication network <b>330</b>. Branch office/branch office communication and central office/central office communication, as well as multi-appliance and/or multi-node communication and bi-directional communication are further within the scope of the disclosure. However, for the sake of simplicity, the disclosure illustrates the network memory system <b>300</b> having the single branch office <b>310</b> and the single central office <b>320</b>, and the respective branch office <b>310</b>/central office <b>320</b> communication.

The communication network <b>330</b> comprises hardware and/or software elements that enable the exchange of information (e.g., voice and data) between the branch office <b>310</b> and the central office <b>320</b>. Some examples of the communication network <b>330</b> are a private wide-area network (WAN), and the Internet. Typically connections from the branch office <b>310</b> to the communication network <b>330</b> (e.g., from the router <b>360</b> and the router <b>390</b>) are ISDN, T1 lines (1.544 Mbps), and possibly broadband connections such as digital subscriber lines (DSL) and cable modems. Other examples are T3 lines (43.232 Mbps), OC3 (155 Mbps), and OC48 (2.5 Gbps), although more costly and more likely used for interconnection at the central office <b>320</b> or as the backbone of the communication network <b>330</b>.

The branch appliance <b>350</b> comprises hardware and/or software elements configured to receive data (e.g., email, files, and databases transactions), determine whether a portion of the data is locally accessible to an appliance (e.g., the central appliance <b>380</b>), generate an instruction based on the determination, and transfer the instruction to the appliance. The branch appliance <b>350</b> also comprises hardware and/or software elements configured to receive an instruction from an appliance (e.g., the central appliance <b>380</b>), process the instruction to obtain data, and transfer the data to a computer (e.g., the computers <b>340</b>). One example of the branch appliance <b>350</b> is described below with respect to <figref idref="DRAWINGS">FIG. 8</figref>. The operations of the branch appliance <b>350</b> are discussed in further detail below in <figref idref="DRAWINGS">FIGS. 4</figref>, <b>5</b>, <b>6</b>, and <b>7</b>A-<b>7</b>B.

Locally accessible data comprises any data transferable to the computer (e.g., the computers <b>340</b> and the central servers <b>370</b>) by an appliance (e.g., the branch appliance <b>350</b> and the central appliance <b>380</b>) without transferring the data over the communication network <b>330</b>. In some examples, the locally accessible data is stored in random access memory (RAM) in the branch appliance <b>350</b>, on a hard drive in the branch appliance <b>350</b>, and a combination of data stored in RAM and on one or more hard drives in the branch appliance <b>350</b>. In another example, the locally accessible data is accessible by the branch appliance <b>350</b> over a communication network (other than the communication network <b>330</b>), such as data stored in a network attached storage (NAS) device that is internal or external to the branch office <b>310</b>. In still another example, the locally accessible data is stored in a database. The database may be stored in RAM, on a hard disk, a combination of RAM and hard disks, in a NAS device, and/or in other optical and flash storage devices.

The instruction comprises any message or signal that indicates to an appliance (e.g., the branch appliance <b>350</b> and the central appliance <b>380</b>) an action to perform with the data. Some examples of the instruction indicate to the appliance to store the data, to retrieve the data, and to forward the data to the computer (e.g., the central servers <b>370</b> and the computers <b>340</b>). The instruction may be explicit, and implicit based on instructions indicating to store or retrieve the data. In some embodiments, the instruction indicates an index within a database for storing and retrieving the data.

The central appliance <b>380</b> comprises hardware and/or software elements configured to receive data, determine whether a portion of the data is locally accessible to an appliance (e.g., the branch appliance <b>350</b>), generate an instruction based on the determination, and transfer the instruction to the appliance. The central appliance <b>380</b> also comprises hardware and/or software elements configured to receive an instruction from an appliance (e.g., the branch appliance <b>350</b>), process the instruction to obtain the data, and transfer the data to a computer (e.g., the central servers <b>370</b>). One example of the central appliance <b>380</b> is described below with respect to <figref idref="DRAWINGS">FIG. 9</figref>. The operations of the central appliance <b>380</b> are discussed in further detail below in <figref idref="DRAWINGS">FIGS. 4</figref>, <b>5</b>, <b>6</b>, and <b>7</b>A-<b>7</b>B.

As illustrated, the branch appliance <b>350</b> is configured in-line (or serially) between the computers <b>340</b> and the router <b>360</b>. The central appliance <b>380</b> is also configured serially between the central server <b>370</b> and the router <b>390</b>. The branch appliance <b>350</b> and the central appliance <b>380</b> transparently intercept network traffic between the computers <b>340</b> and the central servers <b>370</b>. For example, the central appliance <b>380</b> transparently intercepts data sent from the central servers <b>370</b> and addressed to the computers <b>340</b>. The computers <b>340</b> and the central servers <b>370</b> advantageously require no additional configuration because the branch appliance <b>350</b> and the central appliance <b>380</b> operate transparently.

Alternatively, the branch appliance <b>350</b> and the central appliance <b>380</b> are configured as an additional router or gateway. As a router, for example, the branch appliance <b>350</b> appears to the computers <b>340</b> as an extra hop before the router <b>360</b>. In some embodiments, the branch appliance <b>350</b> and the central appliance <b>380</b> provide redundant routing or peer routing with the router <b>360</b> and the router <b>390</b>. Additionally, in the bridge and router configurations, the branch appliance <b>350</b> and the central appliance <b>380</b> provide failure mechanisms, such as, fail-to-open (e.g., no data access) or fail-to-wire (e.g., a direct connection to the router <b>360</b>).

It will be understood that the branch appliance <b>350</b> and the central appliance <b>380</b> perform bi-directional communication. For example, data sent to the branch appliance <b>350</b> from the central appliance <b>380</b> may be stored in a location locally accessible to the central appliance <b>380</b> and in a location locally accessible to the branch appliance <b>350</b>. If the data is to be transferred again from the central appliance <b>380</b> to the branch appliance <b>350</b>, the central appliance <b>380</b> may determine that the data is locally accessible to the branch appliance <b>350</b> and generate an instruction to the branch appliance <b>350</b> to retrieve the data. The central appliance <b>380</b> transfers the instruction to the branch appliance <b>350</b> and the branch appliance <b>350</b> processes the instruction to obtain the data. If later, the branch appliance <b>350</b> is to transfer the entire data back to the central appliance <b>380</b>, the branch appliance <b>350</b> may use the fact that the central appliance <b>380</b> has before transferred the data to the branch appliance <b>350</b>. The branch appliance <b>350</b> therefore determines that the data is locally accessible to the central appliance <b>380</b> and generates an instruction to the central appliance <b>380</b> to retrieve the data. The branch appliance <b>350</b> transmits the instruction to the central appliance <b>380</b> and the central appliance <b>380</b> processes the instruction to obtain the data. Therefore, an appliance (e.g., the branch appliance <b>350</b> and the central appliance <b>380</b>) in the network memory system <b>300</b> advantageously uses data transferred to and from the appliance to reduce network traffic with other appliances in the network memory system <b>300</b>.

The network memory system <b>300</b> advantageously provides increased productivity, reduced IT costs, and enhanced data integrity and compliance. For example, the network memory system <b>300</b> achieves the simple administration of centralized server systems whereby the central servers <b>370</b> store the primary copy of the data. The network memory system <b>300</b> improves application performance and data access in the branch office <b>310</b> and central office <b>320</b> because not every response to a data request travels over the communication network <b>330</b> from the central servers <b>370</b>. The branch appliance <b>350</b> and the central appliance <b>380</b> also store to and retrieve from a local copy of the data for subsequent exchanges of the data.

Additionally, the network memory system <b>300</b> does not cache the data in the traditional sense. The data may be retrieved locally even if the URL or filename for the data is different because the data may be identified by a pattern for the data itself and not by the URL or filename. Furthermore, unlike web caching, the network memory system <b>300</b> ensures that the data is coherent by forwarding messages (e.g., data requests and responses) between the computers <b>340</b> and the central servers <b>370</b>. For example, web caching operates by locally intercepting messages for an authoritative source (e.g., a web server) and responding to the messages such that the web server potentially never sees the messages. In some cases, particularly with dynamic content, the locally cached copy may be stale or out-of-date. Advantageously, the network memory system <b>300</b> provides the data coherency and up-to-date data by the transparent operation of the network memory system <b>300</b> and the principle in which messages are transferred end-to-end (e.g., from the computer <b>340</b> to the central servers <b>370</b>), even though the messages and/or the data may not traverse the communication network <b>330</b>.

The network memory system <b>300</b> does not have the higher cost of distributed server systems because the branch appliance <b>350</b> and the central appliance <b>380</b> provide benefits across all applications and displace several distributed devices and caches, particularly in multiple branch implementations. In some embodiments, the branch appliance <b>350</b> and the central appliance <b>380</b> provide internal storage for a secondary copy of the data. The network memory system <b>300</b> also reduces the hardware and license costs for the branch office <b>310</b> and the central office <b>320</b> by eliminating the need for the numerous distributed devices. Further, the network memory system <b>300</b> minimizes the security vulnerabilities and patching activities commonly associated with the distributed systems. Management of the branch appliance <b>350</b> and the central appliance <b>380</b> is simpler than the management of a remote distributed server. Unlike remote servers, there is no need to configure user accounts, permissions, and authentication schemes on the branch appliance <b>350</b> and the central appliance <b>380</b>.

<figref idref="DRAWINGS">FIG. 4</figref> illustrates a message sequence chart for the network memory system <b>300</b> where a response data <b>425</b> to a data request <b>410</b> is not locally accessible to the branch appliance <b>350</b>, in an exemplary implementation of the invention. In this example, the computer <b>340</b> transmits the data request <b>410</b> through the branch appliance <b>350</b> and the central appliance <b>380</b> to the central server <b>370</b>. Some examples of the data request <b>410</b> are requests for an email attachment, a file, a web page, and a database query.

In sequence <b>415</b>, the central servers <b>370</b> process the data request <b>410</b>, and in sequence <b>420</b>, the central servers <b>370</b> generate the response data <b>425</b> based on the data request <b>410</b>. Some examples of the response data <b>425</b> are an email message and attachment, a file, a web page, and results retrieved or obtained from the database query. The central servers <b>370</b> then transmit the response data <b>425</b> to the central appliance <b>380</b>. Alternatively, in some embodiments, the central server <b>370</b> addresses the response data <b>425</b> directly to the computer <b>340</b>, however, during transmission, the central appliance <b>380</b> transparently intercepts the response data <b>425</b>. In sequence <b>430</b>, the central appliance <b>380</b> processes the response data <b>425</b> to determine whether a portion of the response data <b>425</b> is locally accessible to the branch appliance <b>350</b>.

<figref idref="DRAWINGS">FIG. 5</figref> illustrates data structures for the network memory system <b>300</b> to determine whether a portion of the data is locally accessible to the branch appliance <b>350</b>, in an exemplary implementation of the invention. The data structures include a fine signature hash table (SHT) <b>505</b>, a coarse signature hash table (SHT) <b>525</b>, and flow history pages (FHPs) <b>545</b>. The fine SHT <b>505</b> includes one or more entries comprising a check field <b>510</b>, a page field <b>515</b>, and a byte field <b>520</b>. The coarse SHT <b>525</b> includes one or more entries comprising a check field <b>530</b>, a page field <b>535</b>, and a byte field <b>540</b>. The FHPs <b>545</b> include one or more pages (e.g., page <b>1</b>-M). Each page (e.g., page N) includes page state information <b>550</b> and stores data <b>555</b>.

An appliance of the network memory system <b>300</b> (e.g., the branch appliance <b>350</b> and the central appliance <b>380</b>) calculates hashes at every byte boundary of a data flow (e.g., the response data <b>425</b>) to be sent across the communication network <b>330</b>. In some embodiments, the data flow includes packets that are in the same Internet Protocol (IP) flow, as defined by the IP header five tuple of source address, source port, destination address, destination port, and protocol. The hashes may be influenced by preceding bytes in the data flow. For example, the hashes are influenced by approximately the n previous bytes, where n determines the fingerprint size. Some examples of calculating the hashes are cyclical redundancy checks (CRCs) and checksums over the previous n bytes of the data flow. In some embodiments, rolling implementations of CRCs and checksums are used where a new byte is added, and a byte from n bytes earlier is removed. To maximize the ability to determine whether a portion of the data flow exists in another appliance in the network memory system <b>300</b>, the hash calculation may span across successive IP packets in the data flow. In other embodiments, the hash calculation ignores patterns that span one or more IP packet boundaries in the data flow, and the hashes are calculated within a single IP packet.

Each calculated hash is filtered by a fine filter <b>560</b> and a coarse filter <b>565</b>. The appliance designates the locations in the data flow which meet the fine and coarse filter criteria as fine and coarse sync-points, respectively. The fine filter <b>560</b> and the coarse filter <b>565</b> have different filter criteria. Typically, the filter criteria for the coarse filter <b>560</b> is more restrictive and may be used to further filter those hashes which pass the fine filter. In other words, the fine filter produces a fine comb of sync-points and the coarse filter produces a coarse comb of sync-points. One example of the filter criteria is the null filter which allows results in sync-points at all locations. In another example, the filter criteria declares a fine sync-point when the top five bits of the hashes are all zeros and a coarse filter criteria which stores or compares hashes when the top ten bits of the hashes are all zeros. The hash at the fine sync-points index the fine SHT <b>505</b> and the hash at the coarse sync-points index the coarse SHT <b>525</b>. For example, the index could be derived from the hash by using a number of low order bits from the hash. The filter criteria affect the sizing of the SHTs <b>505</b> and <b>525</b> and the probability of matching a hash in the SHTs <b>505</b> and <b>525</b>. The more sync-points that are generated the easier repeated data is identified but, the larger the tables (i.e., the SHTs <b>505</b> and <b>525</b>) need to be in order to index a given amount of information for the data flow. Having a coarse and fine table helps optimize this tradeoff. Alternative implementations may use a single table or multiple tables.

The fine SHT <b>505</b> is populated with hashes as the data <b>555</b> (e.g., the response data <b>425</b>) is stored and when the data <b>555</b> is recalled from disk or other locally accessible storage. The fine SHT <b>505</b> finely indexes the data <b>555</b>. In some embodiments, the fine SHT <b>505</b> holds approximately one entry for every 100 bytes of the data <b>555</b>. The coarse SHT <b>525</b> is populated as the data <b>555</b> is stored and is coarsely indexed. For example, the coarse SHT <b>525</b> may hold one entry for approximately every 4 kilobytes (KB) of the data <b>555</b>. The fine SHT <b>505</b> and the coarse SHT <b>525</b> may be considered short term and long term memory index structures, respectively.

The appliance of the network memory system <b>300</b> stores all or part of the calculated hashes in or compares all or part of the hashes to the check field <b>510</b> in the SHTs <b>505</b> and <b>525</b>. For example, the central appliance <b>380</b> verifies a “hit” in the fine SHT <b>505</b> by comparing the entire calculated hash or a number of residual bits of the calculated hash to the check field <b>510</b>. If the central appliance <b>380</b> finds no matching hashes in the fine SHT <b>505</b> or in the coarse SHT <b>525</b>, the central appliance <b>380</b> determines that the response data <b>425</b> is not locally accessible to the branch appliance <b>350</b>. Each calculated hash for the response data <b>425</b> in the fine SHT <b>505</b> and the coarse SHT <b>525</b> is stored or compared depending on the filter criteria for the fine filter <b>560</b> and the coarse filter <b>565</b>.

The appliance of the network memory system <b>300</b> indexes each entry in the fine SHT <b>505</b> and the coarse SHT <b>525</b> to a page (e.g., by setting the page field <b>515</b> and the page field <b>535</b> to address page N) and byte offset (e.g., by setting the byte field <b>520</b> and the byte field <b>540</b> to a byte offset of the data <b>555</b>) in the FHPs <b>545</b>. For example, the central appliance <b>380</b> stores the response data <b>425</b> in the FHPs <b>545</b> at the page pointed to by the page field <b>515</b> and <b>535</b> at the byte offset indicated by the byte field <b>520</b> and <b>540</b>. The byte field <b>520</b> of each hash in the fine SHT <b>505</b> for the response data <b>425</b> points to the start of a fine sync-point. The byte field <b>540</b> of each hash in the coarse SHT <b>525</b> for the response data <b>425</b> points to the start of a coarse sync-point.

In this example, the branch appliance <b>350</b> includes a fine SHT <b>505</b>, a coarse filter <b>525</b>, and a FHP <b>545</b> data structure, and the central appliance <b>380</b> includes a fine SHT <b>505</b>, a coarse filter <b>525</b>, and a FHP <b>545</b> data structure. Each appliance in the network memory system <b>300</b> maintains the separate data structures, with may include separate filter criteria for the fine filters <b>560</b> and the coarse filters <b>565</b>. The page state information <b>550</b>, in the FHP <b>545</b> of each appliance in the network memory system <b>300</b>, includes page parameters, page ownership permissions, peer state, and a list of valid byte ranges for each appliance in the network memory system <b>300</b>. The page state information <b>550</b> tracks the local state of the page (e.g., the FHP <b>545</b> in the branch appliance <b>350</b>, and what parts of the page are used) and the remote state of the page at peers (e.g., the central appliance <b>380</b>, and what part of the page in the branch appliance <b>350</b> is used by the central appliance <b>380</b>).

The branch appliance <b>350</b> and the central appliance <b>380</b> each write the data <b>555</b> to an assigned page (e.g., the page N or the page N+1) and may reference a page assigned to another appliance in the network memory system <b>300</b>. Appliances in the network memory system <b>300</b> may discover and reconcile the FHPs <b>545</b> assigned to other appliances as explained below with regard to <figref idref="DRAWINGS">FIGS. 9 and 10</figref>.

Referring again to <figref idref="DRAWINGS">FIG. 4</figref>, the central appliance <b>380</b> proceeds with the determination that no portion of the response data <b>425</b> is locally accessible to the branch appliance <b>350</b>. In sequence <b>435</b>, the central appliance <b>380</b> generates a store instruction <b>440</b>. The store instruction <b>440</b> indicates to the branch appliance <b>350</b> to store the response data <b>425</b> at an index in a database. The central appliance <b>380</b> attaches the store instruction <b>440</b> to the response data <b>425</b>. The central appliance <b>380</b> then transmits the response data <b>425</b> with the store instruction <b>440</b> to the branch appliance <b>350</b>.

In sequence <b>445</b>, the branch appliance <b>350</b> processes the response data <b>725</b> with the store instruction <b>440</b>. In sequence <b>450</b>, based on the store instruction <b>440</b>, the branch appliance <b>350</b> stores the response data <b>425</b> in the branch appliance <b>350</b> at the index within the database. In this example, the branch appliance <b>350</b> stores the response data <b>425</b> in the FHPs <b>545</b> at the page and at a particular byte offset indicated by the index. In sequence <b>455</b>, the branch appliance <b>350</b> forwards the response data <b>425</b> to the computer <b>340</b>. As discussed previously, the branch appliance <b>350</b> may forward the data to the computer based on explicit and implicit instructions.

<figref idref="DRAWINGS">FIG. 6</figref> illustrates a message sequence chart for the network memory system <b>300</b> where a response data <b>625</b> to a data request <b>610</b> is locally accessible to the branch appliance <b>350</b>, in an exemplary implementation of the invention. In this example, the computer <b>340</b> transmits the data request <b>610</b> to the central servers <b>370</b> through the branch appliance <b>350</b> and the central appliance <b>380</b>. In sequence <b>615</b>, the central servers <b>370</b> process the data request <b>610</b>. In sequence <b>620</b>, the central servers <b>370</b> generate a response data <b>625</b> based on the data request <b>610</b>. The central servers <b>370</b> then transmit the response data <b>625</b> to the central appliance <b>380</b>.

In sequence <b>630</b>, the central appliance <b>380</b> processes the response data <b>625</b> to determine whether a portion of the response data <b>625</b> is locally accessible to the branch appliance <b>350</b>. The central appliance <b>380</b> again generates hashes for the response data <b>625</b>, as previously described with respect to <figref idref="DRAWINGS">FIGS. 4 and 5</figref>. The central appliance <b>380</b> filters the generated hashes through the fine filter <b>560</b> and the coarse filter <b>565</b> to determine fine and/or coarse sync-points. The central appliance <b>380</b> looks up the fine sync-points in the fine SHT <b>505</b> and the coarse sync-points in the coarse SHT <b>525</b>. If any of the hashes for the response data <b>625</b> match (i.e., the check bytes match in either the fine SHT <b>505</b> and/or the coarse SHT <b>525</b>), then additional checks (such as direct forward comparisons and backward memory comparisons between the response data <b>625</b> and the data <b>555</b> in the FHPs <b>545</b>) may also be made to determine the size of the matching region. Further checks using the page state information <b>550</b> determine which portion of the response data <b>625</b> is locally accessible to the branch appliance <b>350</b>.

Based on the determination that the entire response data <b>625</b> is locally accessible to the branch appliance <b>350</b>, in sequence <b>635</b>, the central appliance <b>380</b> generates a retrieve instruction <b>640</b> that indicates to the branch appliance <b>350</b> to retrieve the response data <b>625</b> at an index within the database. The central appliance <b>380</b> then transmits only the retrieve instruction <b>640</b> to the branch appliance <b>350</b>. In this manner, the central appliance <b>380</b> optimizes network traffic over the communication network <b>330</b>. If the retrieve instruction <b>640</b> is smaller in size than the response data <b>625</b>, the central appliance <b>380</b> transmits the retrieve instruction <b>640</b>. If the retrieve instruction <b>640</b> is larger than the response data <b>625</b>, the central appliance <b>380</b> transmits the response data <b>625</b> instead.

In sequence <b>645</b>, the branch appliance <b>350</b> processes the retrieve instruction <b>640</b>. In sequence <b>650</b>, based on the retrieve instruction <b>640</b>, the branch appliance <b>350</b> retrieves the response data <b>625</b> at the index within the database. In sequence <b>655</b>, the branch appliance <b>350</b> forwards the response data <b>625</b> to the computer <b>340</b>.

<figref idref="DRAWINGS">FIG. 7A</figref> and <figref idref="DRAWINGS">FIG. 7B</figref> illustrate a message sequence chart for the network memory system <b>300</b> where a portion of a response data <b>725</b> to a data request <b>710</b> is locally accessible to the branch appliance <b>350</b>, in an exemplary implementation of the invention. The computer <b>340</b> transmits the data request <b>710</b> to the central servers <b>370</b> through the branch appliance <b>350</b> and the central appliance <b>380</b>. In sequence <b>715</b>, the central servers <b>370</b> process the data request <b>710</b>. In sequence <b>720</b>, the central servers <b>370</b> generate a response data <b>725</b> based on the data request <b>710</b>. The central servers <b>370</b> then transmit the response data <b>725</b> to the central appliance <b>380</b>.

In sequence <b>730</b>, the central appliance <b>380</b> processes the response data <b>725</b> to determine whether a portion of the response data <b>725</b> is locally accessible to the branch appliance <b>350</b>. The central appliance <b>380</b> computes hashes for the response data <b>725</b> and filters the hashes through the fine filter <b>560</b> and the coarse filter <b>565</b> to determine any fine and coarse sync-points. The central appliance <b>380</b> then looks up any fine sync-points in the fine SHT <b>505</b> and coarse sync-points in the coarse SHT <b>525</b>. In this example, only a portion of the response data <b>725</b> is locally accessible to the branch appliance <b>350</b>, meaning that although the central appliance <b>380</b> finds at least one match in the SHTs <b>505</b> and <b>525</b>, additional checks (such as the direct forward comparison and the backward memory comparison with the response data <b>725</b> and the data <b>555</b>) determine that only a portion of the response data <b>725</b> is locally accessible to the branch appliance <b>350</b>.

The central appliance <b>380</b> stores the generated hashes for the non-locally accessible portion of the response data <b>725</b> (otherwise known as the deltas) in the SHTs <b>505</b> and <b>525</b>, and stores the deltas in the FHPs <b>545</b>. The central appliance <b>380</b> will transmit the deltas (i.e., the portion of the response data <b>725</b> that is not locally accessible) to the branch appliance <b>350</b>.

In sequence <b>735</b>, the central appliance <b>380</b> generates retrieve and store instructions <b>740</b>. The retrieve instruction indicates to the branch appliance <b>350</b> to retrieve the locally accessible portion of the response data <b>725</b> at an index within the database. The store instruction indicates to the branch appliance <b>350</b> to store the deltas at an index within the database. The store instruction may also indicate to the branch appliance <b>350</b> to store another copy of the portion of the response data <b>725</b> locally accessible to the branch appliance <b>350</b> with the deltas. The entire response data <b>725</b> will then be locally accessible in the database to the branch appliance <b>350</b>. The central appliance <b>380</b> attaches the deltas to the retrieve and store instructions <b>740</b>. The central appliance <b>380</b> then transmits the non-locally accessible portion of the response data <b>725</b> with retrieve and store instructions <b>740</b> to the branch appliance <b>350</b>.

In sequence <b>745</b>, the branch appliance <b>350</b> processes the non-locally accessible portion of the response data <b>725</b> with retrieve and store instructions <b>740</b>. In sequence <b>750</b>, based on the retrieve instruction, the branch appliance <b>350</b> retrieves the locally accessible portion of the response data <b>725</b> at the index in the database. In sequence <b>755</b>, the branch appliance <b>350</b> obtains the response data <b>725</b> from the retrieved locally accessible portion and the transferred deltas (i.e., the transferred non-locally accessible portion of the response data <b>725</b>). In sequence <b>760</b>, based on the store instruction, the branch appliance <b>350</b> stores the deltas (and potentially the retrieve locally accessible portion of the response data <b>725</b>) at the index in the database. In sequence <b>765</b>, the branch appliance <b>350</b> transmits the entire response data <b>725</b> to the computer <b>340</b>.

Alternatively, in addition to the examples in <figref idref="DRAWINGS">FIGS. 4</figref>, <b>5</b>, <b>6</b>, and <b>7</b>A-<b>7</b>B illustrating a request for the data originating from the computer <b>340</b> to the central servers <b>370</b>, the computer <b>340</b> may also transmit data to the branch appliance <b>350</b> addressed to the central servers <b>370</b>. The branch appliance <b>350</b> determines whether a portion of the data is locally accessible to the central appliance <b>380</b>. Then, for example, if the data is locally accessible the central appliance <b>380</b>, the branch appliance <b>350</b> generates a retrieve instruction indicating to the central appliance <b>380</b> to retrieve the data and forward the data to the central server <b>370</b>.

In still further embodiments, the instruction may indicate a plurality of indexes. Referring again to <figref idref="DRAWINGS">FIG. 7B</figref>, in sequence <b>750</b>, based on the retrieve instruction indicating a plurality of indexes for the response data <b>725</b>, the branch appliance <b>350</b> may retrieve the locally accessible portion of the response data <b>725</b> at different locations based on the plurality of index. For example, the branch appliance <b>350</b> may retrieve a portion of the response data <b>725</b> from RAM, a portion from a hard disk, and a portion from a NAS device. Similarly, in sequence <b>760</b>, based on the store instruction indicating a plurality of indexes for the response data <b>725</b>, the branch appliance <b>350</b> may stores the deltas in the database and after obtaining the entire response data <b>725</b>, store the entire response data <b>725</b> in a different location (e.g., in a different location in the database, in a disk drive, or in a NAS device) than the previously locally accessible portion.

<figref idref="DRAWINGS">FIG. 8</figref> illustrates a block diagram of the branch appliance <b>350</b>, in an exemplary implementation of the invention. The branch appliance <b>350</b> includes a processor <b>810</b>, a memory <b>820</b>, a WAN communication interface <b>830</b>, a LAN communication interface <b>840</b>, and a database <b>850</b>. A system bus <b>880</b> links the processor <b>810</b>, the memory <b>820</b>, the WAN communication interface <b>830</b>, the LAN communication interface <b>840</b>, and the database <b>850</b>. Line <b>860</b> links the WAN communication interface <b>830</b> to the router <b>360</b> (in <figref idref="DRAWINGS">FIG. 3</figref>). Line <b>870</b> links the LAN communication interface <b>840</b> to the computers <b>340</b> (in <figref idref="DRAWINGS">FIG. 3</figref>).

The database <b>850</b> comprises hardware and/or software elements configured to store data in an organized format to allow the processor <b>810</b> to create, modify, and retrieve the data. The database <b>850</b> may organize the data to enable the determination of whether a portion of the data is locally accessible to an appliance, and to enable quick retrieval of locally accessible data to the branch appliance <b>350</b>. The hardware and/or software elements of the database <b>850</b> may include storage devices, such as RAM, hard drives, optical drives, flash memory, and magnetic tape. In some embodiments, the branch appliance <b>350</b> implements a virtual memory system with linear addresses, the locally accessible data, and the data structures discussed with respect to <figref idref="DRAWINGS">FIG. 5</figref> in the database <b>850</b>.

<figref idref="DRAWINGS">FIG. 9</figref> illustrates a block diagram of the central appliance <b>380</b>, in an exemplary implementation of the invention. The central appliance <b>380</b> includes a processor <b>910</b>, a memory <b>920</b>, a WAN communication interface <b>930</b>, a LAN communication interface <b>940</b>, and a database <b>950</b>. A system bus <b>980</b> links the processor <b>910</b>, the memory <b>920</b>, the WAN communication interface <b>930</b>, the LAN communication interface <b>940</b>, and the database <b>950</b>. Line <b>960</b> links the WAN communication interface <b>930</b> to the router <b>390</b> (in <figref idref="DRAWINGS">FIG. 3</figref>). Line <b>970</b> links the LAN communication interface <b>940</b> to the central servers <b>370</b> (in <figref idref="DRAWINGS">FIG. 3</figref>). In some embodiments, the branch appliance <b>350</b> and the central appliance <b>380</b> comprise the identical hardware and/or software elements. Alternatively, in other embodiments, the central appliance <b>380</b> may include hardware and/or software elements providing additionally processing, communication, and storage capacity.

Advantageously, the network memory system <b>300</b> improves application performance and data access. In some embodiments, by storing a secondary copy of the data locally accessible to the branch appliance <b>350</b> and the central appliance <b>380</b>, the network memory system <b>300</b> minimizes the effects of latency and reduces network traffic over the communication network <b>330</b> to the central servers <b>370</b>. Additionally, while the central servers <b>370</b> maintain the primary copy of the data, the central servers <b>370</b> potentially do not transfer the actual data over the communication network <b>330</b> for every request/response. Furthermore, accelerated access to the data locally accessible to the branch appliance <b>350</b> and the central appliance <b>380</b> is not limited to a particular application or data context.

In some embodiments, the network memory system <b>300</b> includes a secure tunnel between the branch appliance <b>350</b> and the central appliance <b>380</b>. The secure tunnel provides encryption (e.g., IPsec) and access control lists (ACLs). Additionally, in other embodiments, the secure tunnel includes compression, such as header and payload compression. The secure tunnel may provide fragmentation/coalescing optimizations along with error detection and correction.

<figref idref="DRAWINGS">FIG. 10</figref> illustrates a network memory system <b>1000</b> between a first office <b>1010</b>, a second office <b>1030</b>, and a third office <b>1060</b>, in an exemplary implementation of the invention. The first office <b>1010</b> includes a computer <b>1015</b> and a first network memory appliance (NMA) <b>1020</b>. The second office <b>1030</b> includes a computer <b>1040</b> and a second NMA <b>1050</b>. The third office <b>1060</b> includes a third NMA <b>1070</b> and a server <b>1080</b>. The first office <b>1010</b> is linked to the second office <b>1030</b> and the third office <b>1060</b> (e.g., through routers not shown). The second office <b>1030</b> is also linked the third office <b>1060</b>.

The first NMA <b>1020</b>, the second NMA <b>1050</b>, and the third NMA <b>1070</b> comprise hardware and/or software elements, similar to the branch appliance <b>350</b> and the central appliance <b>380</b>, configured to receive data, determine whether the data is locally accessible to an appliance, generate an instruction based on the determination, and transfer the instruction to the appliance. The first NMA <b>1020</b>, the second NMA <b>1050</b>, and the third NMA <b>1070</b> also comprise hardware and/or software elements configured to receive an instruction from an appliance, process the instruction to obtain data, and transfer the data to a computer.

Advantageously, in this multi-office example, the network memory system <b>1000</b> provides for locally accessible data in each office. The first NMA <b>1020</b>, the second NMA <b>1050</b>, and the third NMA <b>1070</b> receive data, potentially destined for a computer and/or server in another office, and determine whether a portion of the data is locally accessible to an NMA in that office. To further enhance operation and the exchange of data between the first NMA <b>1020</b>, the second NMA <b>1050</b>, and the third NMA <b>1070</b>, each NMA performs a discovery and reconciliation. During discovery and reconciliation the virtual memory map of the network memory system <b>1000</b> is updated. For example, each NMA updates the pages of the FHPs <b>545</b> in the NMA with references for data locally accessible in the network memory system <b>1000</b> and to which NMA the data is locally accessible.

<figref idref="DRAWINGS">FIG. 11</figref> illustrates a message sequence chart for the network memory system <b>1000</b> for discovery and reconciliation, in an exemplary implementation of the invention. In this example, the computer <b>1015</b> in the first office <b>1010</b> transmits data to the first NMA <b>1020</b> for the first time addressed to the computer <b>1040</b> in the second office <b>1030</b>. The first NMA <b>1020</b> transmits the data with a store instruction to the second NMA <b>1050</b> indicating to store the data in a database in the second NMA <b>1050</b>. In sequence <b>1110</b>, the second NMA <b>1050</b> stores the data in the database, and the second NMA <b>1050</b> transmits the data to the computer <b>1040</b>.

The computer <b>1015</b> in the first office <b>1010</b> then transmits the same data to the first NMA <b>1020</b> addressed for the first time to the server <b>1080</b> in the third office <b>1060</b>. The first NMA <b>1020</b> transmits the data with a store instruction to the third NMA <b>1070</b> indicating to store the data in a database in the third NMA <b>1070</b>. In the sequence <b>1115</b>, the third NMA <b>1070</b> stores the data in the database, and the third NMA <b>1070</b> transmits the data to the server <b>1080</b>.

In sequence <b>1120</b>, <b>1125</b>, and <b>1130</b>, the first NMA <b>1020</b>, the second NMA <b>1050</b>, and the third NMA <b>1070</b> perform discovery and reconciliation including update the virtual memory map. In this example, the first NMA <b>1020</b>, the second NMA <b>1050</b>, and the third NMA <b>1070</b> exchange information (e.g., the page state information <b>550</b>) about which parts of the FHPs <b>545</b> each NMA has available locally. For example, to update the FHPs <b>545</b> in the second NMA <b>1050</b>, the second NMA <b>1050</b> performs a discovery and reconciliation with the first NMA <b>1020</b> and the third NMA <b>1070</b>. Similarly, each NMA performs discovery and reconciliation with every other peer NMA.

During the discovery and reconciliation between the second NMA <b>1050</b> and the first NMA <b>1020</b>, for example, the second NMA <b>1050</b> discovers from the first NMA <b>1020</b> that the data (transmitted from the computer <b>1015</b> to the computer <b>1040</b> and the server <b>1080</b>) is locally accessible to the third NMA <b>1070</b>. The FHPs <b>545</b> of the first NMA <b>1020</b> include references to the data (e.g., in the page state information <b>550</b>) and because the first NMA <b>1020</b> transferred the data to the third NMA <b>1070</b>, the FHPs <b>545</b> indicate that the data is locally accessible to the third NMA <b>1070</b>. The second NMA <b>1050</b> reconciles the references for the data in the FHPs <b>545</b> and further indicates that data is locally accessible to the third NMA <b>1070</b>.

Referring again to <figref idref="DRAWINGS">FIG. 11</figref>, in sequence <b>1135</b>, after the discovery and reconciliation in sequences <b>1120</b>, <b>1125</b>, and <b>1130</b>, the computer <b>1040</b> in the second office <b>1030</b> transmits the data addressed to the server <b>1080</b> in the third office <b>1060</b>. The data is intercepted by the second NMA <b>1050</b>, and in sequence <b>1140</b>, the second NMA <b>1050</b> determines whether a portion of the data is locally accessible to the third NMA <b>1070</b>. Since the discovery and reconciliation, the FHPs <b>545</b> in the second NMA <b>1050</b> indicates that data is locally accessible to the third NMA <b>1070</b>. In sequence <b>1145</b>, the second NMA <b>1050</b> generates a retrieve instruction indicating to the third NMA <b>1070</b> to retrieve the data from an index within the database. The second NMA <b>1050</b> transfers the retrieve instruction to the third NMA <b>1070</b>.

In sequence <b>1150</b>, the third NMA <b>1070</b> processes the retrieve instruction. In sequence <b>1155</b>, based on the retrieve instruction, the third NMA <b>1070</b> retrieves the data at the index within the database. In sequence <b>1160</b>, the third NMA <b>1070</b> forwards the data to the server <b>1080</b>.

Therefore, the network memory system <b>1000</b> provides improved application performance and data access between the first office <b>1010</b>, the second office <b>1030</b>, and the third office <b>1060</b>. The network memory system <b>1000</b> provides access to locally accessible data, similar to distributed servers, without the complex management involved with replication and synchronization of the data among the distributed servers. Additionally, the network memory system <b>1000</b> reduces network traffic between the offices. Furthermore, discovery and reconciliation provides performance advantages by periodically or continuously updating the FHPs <b>545</b> in each NMA.

In further embodiments, it may be desirable to store specific data at the branch appliance <b>350</b> before the data is requested at a branch office <b>310</b>. For example, the first download of a software update over the communication network <b>330</b> at a branch office <b>310</b> may require several minutes. To make the first download of the software update faster, the software update may be downloaded previously to the branch appliance <b>350</b>. To trigger the previous download, a pre-positioning command may be executed.

<figref idref="DRAWINGS">FIG. 12</figref> depicts a diagram of an exemplary network memory system <b>1200</b> in which various embodiments of the invention may be practiced. Like the network memory system <b>300</b> depicted in <figref idref="DRAWINGS">FIG. 3</figref>, the network memory system <b>1200</b> comprises a central office <b>320</b>, a communication network <b>330</b>, and a branch office <b>310</b>. In the network memory system <b>1200</b>, the branch appliance <b>350</b> further comprises a pre-positioning receiver <b>1206</b> and a memory subsystem <b>1204</b>. Similarly, the central appliance <b>380</b> also comprises a memory subsystem <b>1204</b>. According to various embodiments, the central appliance <b>380</b> may additionally comprise a pre-positioning receiver <b>1206</b>. In some embodiments, the central appliance <b>380</b> and/or the memory subsystem <b>1204</b> comprises the pre-positioning controller <b>1202</b>.

In exemplary embodiments, the pre-positioning controller <b>1202</b> is configured to execute a pre-positioning command. In one example, a network administrator may generate a pre-positioning command to position data at the branch appliance <b>350</b> such that the data is locally accessible at the branch office <b>310</b>. The data to be pre-positioned may include, for example, software updates, frequently used files, or other data that will likely be requested at the branch office <b>310</b>.

In another example, a software update for computers <b>340</b> in the branch office <b>310</b> becomes available at the central servers <b>370</b> in the central office <b>320</b>. The network administrator in the central office <b>320</b> may wish to provide the update to the branch office <b>310</b> at a time when there is only a small amount of data being communicated over communication network <b>330</b>, for example, at night.

When data is pre-positioned in a branch appliance <b>350</b>, the data is received from the central appliance <b>380</b> and/or retrieved from the memory subsystem <b>1204</b> without a request first being received from one of the computers <b>340</b>. Within the network memory system <b>1200</b>, these actions store the data and/or overwrite older data according to an LRU or FIFO algorithm within the memory subsystem <b>1204</b>. This results in faster retrieval of the data if it is requested by one of the computers <b>340</b>. By pre-positioning the update when very little data is communicated, network performance may be enhanced when one of the computers <b>340</b> first requests the update. In various embodiments, rather than an update being pre-positioned, other types of data, including, but not limited to, files, directories, or the like may be pre-positioned at the branch appliance <b>350</b>.

The pre-positioning controller <b>1202</b> may comprise a graphical user interface configured to receive input from the network administrator. According to various embodiments, the graphical user interface may allow the network administrator to generate a pre-positioning command or script indicating a time of transmission of the data. The time of transmission of the data is defined as the time at which the network administration indicates that the data should be sent to the branch office <b>310</b>. For example, a network administrator may indicate that an update is to be transmitted to the branch office <b>310</b> at 2 A.M., when very little traffic is likely to occur over communication network <b>330</b>.

In one example, the pre-positioning controller <b>1202</b> receives the pre-positioning command over an application program interface (API). The pre-positioning controller <b>1202</b> can provide a customized API or utilize a standard API. In another example, the pre-positioning controller <b>1202</b> receives the pre-positioning command from an operating system or other application. Those skilled in the art will appreciate that there may be many methods of which the pre-positioning controller <b>1202</b> receives the pre-positioning command from a user (e.g., network administrator).

According to various embodiments, the pre-positioning controller <b>1202</b> may be further configured to execute a pre-positioning command according to a schedule. For example, the pre-positioning command may be executed daily at 2 A.M. In some embodiments, multiple pre-positioning commands may be executed simultaneously. Further, the schedule may instruct the pre-positioning controller <b>1202</b> to execute the pre-positioning command at different times for different pre-positioning receivers <b>1206</b>. For example, the pre-positioning command may be executed at different times based on time zones. For example, a software update may be sent to a branch office <b>310</b> in Germany at 3 AM Central European Time (CET) and another branch office <b>310</b> in China at 3 AM China Coast Time (CCT). In alternate embodiments, separate pre-positioning commands based on each of the time zones maybe executed. The schedule allows a network administrator to position data in the branch office <b>310</b> when a small amount of data is transferred via the communication network <b>330</b> to the branch office <b>310</b>.

According to some embodiments, the pre-positioning command comprises a script configured to instruct the pre-positioning controller <b>1202</b> to execute the pre-positioning command. The script may be provided by a user (e.g., the user writes the script) or the script may be generated automatically.

The pre-positioning controller <b>1202</b> may be implemented as part of one or more of the central servers <b>370</b>. According to alternative embodiments, the pre-positioning controller <b>1202</b> may be implemented as part of the central appliance <b>380</b>. The pre-positioning controller <b>1202</b> may comprise instructions stored in a memory, wherein the instructions are executable by a processor. The instructions may be implemented or stored as software, hardware, or the like.

Memory subsystems <b>1204</b> may be located in the central appliance <b>380</b> and/or in the branch appliance <b>350</b>, and are configured to store data passing through the communication network <b>330</b>. The memory subsystems <b>1204</b> may comprise one or more types of memory, including, but not limited to, read-only memory (ROM), random access memory (RAM), FLASH memory, hard disk, NAS device, or the like. In some embodiments, the memory subsystems <b>1204</b> may, be configured to store data and/or overwrite older data according to a first-in-first-out (FIFO) or least recently used (LRU) algorithm. The data may be transmitted from the branch appliance <b>350</b> or the central appliance <b>380</b>, or vice-versa.

The pre-positioning receiver <b>1206</b> is configured to receive data transmitted according to the pre-positioning command executed by the pre-positioning controller <b>1202</b>. In some embodiments, the pre-positioning receiver <b>1206</b> may be implemented as a phantom account or virtual client. The pre-positioning receiver <b>1206</b> may not be associated with any of the computers <b>340</b> or other physical object at the branch office <b>310</b>. To illustrate, according to various embodiments, the pre-positioning receiver <b>1206</b> may comprise a File Transfer Protocol (FTP) server, a Hypertext Protocol (HTP) server, a file system server, or the like. Further, the pre-positioning receiver <b>1206</b> may comprise a virtual machine to implement these services.

The pre-positioning receiver <b>1206</b> may be a part of the branch appliance <b>350</b> and/or the central appliance <b>380</b>. In alternative embodiments, the pre-positioning receiver <b>1206</b> may be associated with one of the computers <b>340</b> and/or one of the central servers <b>370</b>. In some embodiments, the pre-positioning receiver <b>1206</b> may be configured to store data associated with the pre-positioning command. In alternative embodiments, the pre-positioning receiver <b>1206</b> may be configured to delete the received data upon receipt.

In operation, the network administrator, using an interface at the pre-positioning controller <b>1202</b>, inputs a pre-positioning command to pre-position data that may be later requested by the computer <b>340</b>. When the pre-positioning command is executed, data associated with the pre-positioning command is transmitted from the pre-positioning controller <b>1202</b> or the central servers <b>370</b> to the central appliance <b>380</b>. According to various embodiments, the central appliance <b>380</b> may determine whether the data or a portion of the data is locally accessible to the computers <b>340</b> at the branch appliance <b>350</b>. If the data is locally accessible, the central appliance <b>380</b> may transmit a retrieve instruction indicating the data (or portion of the data) to the branch appliance <b>350</b>. If the data is not locally accessible at the branch appliance <b>350</b>, the central appliance <b>380</b> may transmit the data (or the portion of the data) literally to the branch appliance <b>350</b>.

The branch appliance <b>350</b>, upon receiving the data and/or retrieve instruction, stores the data in the memory subsystem <b>1204</b> according to an LRU or FIFO algorithm. Thus the data sent according to the pre-positioning command is locally accessible at the branch office <b>310</b>. If one of the computers <b>340</b> requests the data, the branch appliance <b>350</b> retrieves the data locally from the memory subsystem <b>1204</b> associated with the branch appliance <b>350</b>. Thus, the data need not be communicated across the communication network <b>330</b> if the pre-positioning command has been executed.

The data packets, before reaching the pre-positioning receiver <b>1206</b>, pass through the memory subsystem <b>1204</b>. The branch appliance <b>350</b> stores and indexes the data packets in the memory subsystem <b>1204</b>. The pre-positioning receiver <b>1206</b> may receive the data.

<figref idref="DRAWINGS">FIG. 13</figref> depicts a block diagram of a pre-positioning command <b>1300</b> according to exemplary embodiments. In the embodiment shown, the pre-positioning command <b>1300</b> may include information such as a file or directory <b>1305</b>, a time of transfer <b>1310</b>, a pre-positioning receiver identifier <b>1315</b>, and an optional schedule <b>1320</b>.

The file or directory <b>1305</b> may comprise a copy of the file or directory to be pre-positioned. The file or directory <b>1305</b> may be received from a network administrator using a graphical user interface and/or be automatically generated by one or more of the central servers <b>370</b>. For example, one of the central servers <b>370</b> may receive a software update and determine whether to transmit the update to the computers <b>340</b>. In other embodiments, an identifier such as a path or location may be associated with the file or directory <b>1305</b> to be transferred from the central office <b>320</b> to the branch office <b>310</b>.

The time of transfer <b>1310</b> indicates a time at which the file or directory <b>1305</b> is to be pre-positioned at the branch office <b>310</b>. The time of transfer <b>1310</b> may be represented as a time stamp, a countdown, an elapsed time, or the like. The time of transfer <b>1310</b> may be optional in embodiments if the pre-positioning command <b>1300</b> is executed immediately upon receipt.

The information associated with the pre-positioning receiver identifier <b>1315</b> identifies one or more pre-positioning receivers <b>1206</b>. The pre-positioning receivers <b>1206</b> associated with the pre-positioning command <b>1300</b> may be selected by a network administrator or be selected automatically based on a previous selection by the network administrator. In some embodiments, the pre-positioning receivers <b>1206</b> may be selected based on the type of the file or directory <b>1305</b> being transferred.

Optionally, the schedule <b>1320</b> may be included in the pre-positioning command <b>1300</b>. The schedule <b>1320</b> indicates two or more scheduled transmissions of the file or directory <b>1305</b>. The schedule may be periodic, such as daily at 2 A.M.

<figref idref="DRAWINGS">FIG. 14</figref> depicts a flowchart illustrating a process <b>1400</b> performed by a pre-positioning controller, such as pre-positioning controller <b>1202</b>, for pushing data to a pre-positioning receiver <b>1206</b>, according to exemplary embodiments.

In a step <b>1402</b>, a pre-positioning command is executed. As discussed herein, the pre-positioning command instructs the pre-positioning controller to transfer a file or directory to one or more of the pre-positioning receivers.

In a step <b>1404</b>, data packets associated with the file or directory are transmitted according to the pre-positioning command to the pre-positioning receiver at a specified time. The specified time may, according to some embodiments, be the time of transfer or the time at which the pre-positioning command is received from a network administrator. The data packets may be generated by the central appliance as discussed herein. The data packets may comprise literal data and/or retrieve instructions. The data packets are transmitted via the communication network to the pre-positioning receiver.

At a step <b>1406</b>, one of the computers may request the file or directory. A determination is made as to whether the file or directory has changed since the file or directory was transmitted to the branch office. If the file or directory has changed, the changed file or directory is transmitted to the branch appliance in a step <b>1408</b> according to the processes discussed herein.

At a step <b>1410</b>, a retrieve instruction is transmitted to the branch appliance according to the methods described herein.

At a step <b>1412</b>, a determination is made as to whether the pre-positioning command is scheduled to occur again or if the pre-positioning command is a one-time command. If the pre-positioning command is scheduled to occur again, the process returns to step <b>1404</b>.

<figref idref="DRAWINGS">FIG. 15</figref> depicts a message sequence chart <b>1500</b> of the signals transferred upon execution of a pre-positioning command according to exemplary embodiments. The signals are transferred between a pre-positioning controller <b>1202</b>, a central appliance <b>380</b>, a branch appliance <b>350</b>, and a pre-positioning receiver <b>1206</b>.

At <b>1502</b>, a pre-positioning command <b>1300</b> is executed by the pre-positioning controller <b>1202</b>. The pre-positioning controller <b>1202</b> addresses data associated with the pre-positioning command <b>1300</b> to the pre-positioning receiver <b>1206</b>.

At <b>1504</b>, the central appliance <b>380</b> receives the data, stores, and/or indexes the data and generates data packets based on the processes described herein. At <b>1506</b>, the central appliance <b>380</b> generates data packets that will be transmitted to the branch appliance <b>350</b> via the communication network <b>330</b>.

At <b>1508</b>, the branch appliance <b>350</b> stores and indexes the data packets in the memory subsystem <b>1204</b> according to the process described herein. The file or directory <b>1305</b> is positioned in network memory so that if the file or directory <b>1305</b> is requested by one of the computers <b>340</b>, the file or directory <b>1305</b> may be retrieved from the memory subsystem <b>1204</b>. At <b>1510</b>, the pre-positioning receiver <b>1206</b> receives the file or directory <b>1305</b> from the branch appliance <b>350</b>. Because the computers <b>340</b> do not access the pre-positioning receiver <b>1206</b> to retrieve the file or directory <b>1305</b>, the pre-positioning receiver <b>1206</b> may optionally delete the received file or directory <b>1305</b>. It is understood that additional communications, such as acknowledgements, may be transferred in the message sequence chart <b>1500</b>.

According to various embodiments, the central appliance <b>380</b> may perform actions described in connection with the branch appliance <b>350</b> and vice-versa. Further, data may be pre-positioned in more than one branch appliance <b>350</b>.

The above-described functions can be comprised of executable instructions that are stored on storage media. The executable instructions can be retrieved and executed by a processor. Some examples of executable instructions are software, program code, and firmware. Some examples of storage media are memory devices, tape, disks, integrated circuits, and servers. The executable instructions are operational when executed by the processor to direct the processor to operate in accord with the invention. Those skilled in the art are familiar with executable instructions, processor(s), and storage media.

The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.